Wall adaptors for adapting mains power to provide supply power to consumer devices and/or battery charge power for rechargeable portable devices are well known. Such wall adapters have been used for many years for charging mobile rechargeable devices like for example cell phones or shavers. Such portable devices are delivered to customers accompanied by a wall adaptor, which is to be connected at the input side to the available mains power, usually 110 V or 230 V AC. The output side of the adaptor provides a supply voltage and/or current that is suitable for the respective portable device, i.e. which is according to a supply power requirement of the portable device. Commonly, such adaptors have an input circuit for receiving the mains input power and providing input supply power to a power converter circuit. Such a circuit has a power switch device coupled to the input supply power and a power inductance coupled to the power switch device. Furthermore, an output circuit is coupled to the power inductance to provide the supply power for the portable device. A controller is included for controlling the power switch device, i.e. regularly switching the power switch device on and off at a switching frequency to generate input current pulses in the power inductance. The output circuit draws output current from the power inductance, for example via a secondary inductance magnetically coupled to the power inductance. The various components and the control of the switching is designed according to a supply power requirement of the portable device.